The invention lies in the telecommunications field. More specifically, the invention relates to a method and a configuration for transmitting data via a radio interface in a radio communications system, in particular in a mobile radio system.
In radio communications systems, messages (for example voice, image information, or other data) are transmitted using electromagnetic waves. The electromagnetic waves are thereby radiated at carrier frequencies which lie in the frequency band that is provided for the respective system. In the GSM (Global System for Mobile Communications), the carrier frequencies lie in the 900 MHz range. For future radio communications systems, for example the UMTS (Universal Mobile Telecommunication System) or other 3rd generation systems, frequencies in the approximately 2 GHz frequency band are provided.
The irradiated electromagnetic waves are attenuated owing to losses resulting from reflection, refraction and irradiation due to the curvature of the earth and the like. As a result, the reception power which is available at the receiving radio station drops. The attenuation is location-dependent and, in the case of moving radio stations, also time-dependent.
Between a transmitting and a receiving radio station there is a radio interface over which data is transmitted using the electromagnetic waves. In the GSM mobile radio system, subscriber separation is carried out using a time division multiplex method, the so-called TDMA (Time Division Multiple Access) method which is used in combination with a frequency division multiplex method FDMA (Frequency Division Multiple Access).
In the GSM mobile radio system as is known, inter alia, from J. Biala, xe2x80x9cMobilfunk und intelligente Netzexe2x80x9d [Mobile Radio and Intelligent Networks], Vieweg Verlag [publishing house], 1995 in particular pages 80 and 269, and from P. Smolka xe2x80x9cGSM-Funkschnittstellexe2x80x94Elemente und Funktionen [GSM Radio Interfacexe2x80x94Elements and Functions]xe2x80x9d telekom praxis, No. 4/93, pp. 17-24, in particular FIGS. 4 and 5, a TDMA frame is divided into 8 timeslots. Data from communications links and/or signaling information is transmitted as radio blocks, so-called bursts, in the timeslots. Midambles with known symbols are transmitted within a radio block. These midambles can be used in the manner of training sequences for receive-end tuning of the radio station. The receiving radio station uses the midambles to estimate the channel pulse responses for various transmission channels. Because the transmission properties of the mobile radio channel are location-dependent and frequency-dependent, the receiving radio station can equalize the received signal using this training sequence.
The TDMA subscriber separation method used in the GSM mobile radio system has been developed and dimensioned for the transmission of information with a relatively low data rate. It also has a very restricted degree of flexibility when allocating data rates to a subscriber.
However, in future radio communications systems, and in particular third generation mobile radio systems, high data rates and individual, flexible allocation of transmitter capacities to communications links are desired. Furthermore, mixed operation of different services and data rates and asymmetry of the data rates and of the traffic volume such as, for example, the downlink and uplink (reverse and forward directions) in Internet applications are to be supported.
International PCT publication WO 97/08861 (see U.S. Pat. Nos. 5,768,269 and 5,793,759) discloses an configuration and a method for the bidirectional transmission of digital data over different transmission media. Here, data from a plurality of sources are subjected to a time division multiplex process in timeslots and to coding using orthogonal codes. The coded data are transmitted in frames between central and remote units, the frames being synchronized by means of a transmission interval without data.
European published patent application EP 0 767 557 A1 (see U.S. Pat. No. 5,838,672) discloses a time frame and timeslot structure based on a known TDMA subscriber separation method such as is used in the GSM mobile radio system described above. Here, a training sequence is embedded in a timeslot and surrounded by two data blocks.
The object of the invention is to provide a method and a configuration for data transmission via a radio interface in a radio communications system which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and which enables a flexible and dynamically configurable time division multiplex structure for transmitting data in the downlink direction.
With the above and other objects in view there is provided, in accordance with the invention, a method of transmitting data over a radio interface in a mobile radio system, which comprises:
transmitting data of at least one communications link in a downlink direction from a base station to at least one radio station in radio blocks of a time division multiplex method organized in time frames;
periodically transmitting, within a time frame, training sequences and after a respective training sequence transmitting the radio block of at least one of the communications links, whereby the training sequences are transmitted with a constant transmission power higher than an average transmission power for the radio blocks.
In other words, the invention relates to a method and a base station for transmitting data in the downlink direction over a radio interface in a radio communications system. A base station transmits the data from at least one communications link in the downlink direction to a radio station in radio blocks in accordance with a time division multiplex method. Within a time frame, training sequences are transmitted in periodic fashion and after a respective training sequence the radio block of at least one of the communications links is transmitted. Here, the training sequences are transmitted with a constant transmission power which is higher than an average transmission power for the radio blocks.
This method according to the invention has the advantage that the times for the switching on and off of the transmitter and for the decay of the transmission channels are dispensed with, as a result of which the time component used for transmitting data can be increased. As a further advantage, this method permits the changes of the transmission properties on the radio link to be continuously detected by means of the radio station, and permits the radio station to carry out equalization of the received signals so that, for example, transmission of data is made possible even at higher speeds of the radio station which is embodied as a mobile station of a mobile radio system.
The fact that the training sequences at the transmitting base station end are transmitted with a constant transmission power which is greater than the average transmission power for the data enables the radio station to make precise channel estimations regarding the transmission properties independently of the location and of the power regulation for other radio stations whose data are transmitted in the same radio block or in other radio blocks between the training sequences. In addition, the higher transmission power results in an improvement of the average signal-to-noise ratio when the training sequences are received in the radio station.
In accordance with an added feature of the invention, the radio station interpolates and/or extrapolates the channel estimation from at least two training sequences. The interpolation and/or extrapolation is carried out here for all components of the multipath delay occurring during the transmission on the radio interface which can be resolved chronologically. This refinement has the advantage that the variation in the timing of the transmission properties over the radio blocks can be adjusted with the data intended for the radio station, in which case the extrapolation from the receiving radio station also enables limited predictions to be made about future transmission properties on the radio link. When there are two or more training sequences, linear interpolation and/or extrapolation are possible, whereas when there are three training sequences per timeslot quadratic interpolation and/or extrapolation can be carried out.
An advantageous adjustment of the equalization of the received signals can also be carried out permanently by means of the radio station in which these channel estimations are made on the basis of all the training sequences transmitted by the base station and the changing transmission properties on the radio link are detected by means of an interpolation and/or extrapolation.
In accordance with an additional feature of the invention, the data of a first communications link to the radio station and from other communications links to other radio stations are combined in a radio block. This refinement permits flexible allocation of the transmission capacity on the transmission route to the individual communications links in comparison with the rigid allocation of, in each case, one communications link to one radio block which is transmitted in an interval between two training sequences.
In addition, according to one development of this embodiment the amount of data of the respective first communications link and of the other communications links can advantageously be varied within the radio block as a function of the required transmission capacity. This permits the allocation of data rates to the individual communications links to be made flexible and dynamic, as a result of which, for example, a mixed operation with different services with different data rates or else even a mixed operation of packet-oriented and connection-oriented services is also made possible.
In addition, with such flexible and dynamic allocation of transmission capacities to communications links, in transmission pauses during the first communications link, the unused transmission capacity can be used dynamically by one or more other communications links for transmitting data, as a result of which the effective transmission capacity on the radio link is advantageously increased further.
A further increase in the transmission capacity or in the error protection can, in accordance with another feature of the invention, also be obtained by means of a shortening of the training sequences in comparison with a training sequence which is configured for a customary multipath propagation. This can be carried out, for example, as a function of the size of the radio cell or when there are only a small number of obstacles on the radio link, as a result of which the delay spread, i.e. the longest possible delay time with which a data item can unambiguously be received from the receiving radio station given multipath propagation, is significantly reduced. The transmission capacity which becomes free can in turn additionally be used for transmitting data or for error protection.
In accordance with a further feature of the invention, the data of the first communications link are provided with, in each case, one or more codes for different data sections. The code used here can be a Walsh code which is very suitable owing to its orthogonality and the simple processing of the coded signals.
A code sequence has the amplitude and the phase of a data item of a communications link applied to it, as a result of which a plurality of code sequences which are each assigned to different communications links can be transmitted simultaneously. The sum of the respective discrete time values is subsequently used to modulate the basic pulses which are to be transmitted. At the receive end, the individual received basic pulses are determined and the orthogonal code sequences are separated again by means of a code transformation. The advantage of the coding in comparison with direct transmission of the information as isolated data items (basic pulses) is that averaging of the faults over the length of code sequences occurs. To modulate the data, known forms of modulation, for example BPSK, QPSK etc. can be used.
If the basic pulses are transmitted by the base station with a fixed basic pulse repetition rate clock, the radio station can, according to a further refinement, receive and evaluate these basic pulses by means of a discontinuous transversal filter. The use of a discontinuous transversal filter also enables the basic pulses of one or more base stations which are causing interference in the surroundings of the radio station to be eliminated. In a cellular environment this permits the signal-to-noise ratio at the location of the radio station to be improved considerably.
The discontinuous transversal filter permits a receiver device to be implemented favorably in terms of expenditure. Depending on the dimensioning and the expenditure incurred on the transversal filtering, the method is significantly better for compensating transmission distortions which have previously been taken into account only approximately.
For the transmission it is possible to use, on principle, any desired basic pulses such as Gaussian or chronologically limited sin(x)/x-shaped basic pulses and/or bandwidth-increasing basic pulses which, in the simplest case, are constructed from a train of simple basic pulses.
With the above and other objects in view there is also provided, in accordance with the invention, a base station in a mobile radio communications system wherein data are transmitted over a radio interface in the mobile radio communications system. The data of at least one communications link are transmitted in a downlink direction to at least one radio station in radio blocks of a time division multiplex method organized in time frames. The improved base station comprises:
a device programmed to periodically insert training sequences into a respective time frame, the training sequences being transmitted with a constant transmission power which is higher than an average transmission power for the radio blocks; and
a transmitter device for transmitting the radio block of at least one of the communications links following a respective training sequence.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and configuration for transmitting data over a radio interface in a radio communications system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.